ACTA AMAZONICA http://dx.doi.org/10.1590/1809-4392201501214 Foregut morphology of Macrobrachium carcinus (Crustacea, Decapoda, Palaemonidae) Jô de Farias LIMA1*, Jamile da Silva GARCIA2, Marcos TAVARES3 1 Brazilian Agricultural Research Corporation - Embrapa Amapá, Rodovia Juscelino Kubitschek, km 5, n°2600, CEP: 68906-970, Caixa Postal 10 – Macapá, Amapá, Brazil. 2 University of Amapá, Fishing Engineering Course, Av. Presidente Vargas, nº 650, CEP: 68900-000 Macapá, Amapá, Brazil. 3 Museum of Zoology, University of São Paulo, Av. Nazaré, 481, Ipiranga, 04263-000 - São Paulo, São Paulo, Brazil. * Corresponding author: [email protected] ABSTRACT Macrobrachium carcinus is a Brazilian native prawn with recognized potential for use in aquaculture activities. The aim of this study was to describe and illustrate in detail the morphology of the M. carcinus foregut. The foregut comprises the mouth, esophagus and stomach. It is lined by a simple cylindrical epithelium overlain by chitinous cuticle. The cardiac chamber is well supplied with muscles and lined with chitin thickened in places to form a complex, articulating set of ossicles. The ossicles and setae inside the cardiac chamber seem to direct the food movement through the cardiac chamber and sort the food according to particle size as digestion takes place. Twenty-one basic ossicles were observed in the stomach of M. carcinus and are divided into seven categories, reflecting their presumed functional roles. The significance of these morphological features is discussed in terms of its implication in feeding management that can support future commercial farms of this important fishery resource. KEYWORDS: Freshwater prawn, aquaculture, digestive system, feeding management. Morfologia do estômago do camarão Macrobrachium carcinus (Crustacea, Decapoda, Palaemonidae) RESUMO Macrobrachium carcinus é uma espécie nativa com reconhecido potencial para uso em cultivos aquícolas, porém com poucas informações sobre suas estratégias alimentares. O objetivo deste estudo foi descrever e ilustrar em detalhes a morfologia do estômago de M. carcinus e fazer uma breve associação com seu hábito alimentar. O trato digestivo compreende a boca, esôfago e estômago (câmara cardiáca e câmara pilórica) o qual é revestido por um epitélio cilíndrico simples recoberta por uma fina cutícula quitinosa. A câmara cardíaca é bem provida de músculos e margeada por quitina espessada em áreas formando um conjunto complexo de ossículos articulados. Os ossículos e cerdas no interior da câmara cardíaca parecem dirigir a circulação de alimentos através da câmara cardíaca e triar o alimento de acordo com o tamanho de partícula no decorrer da digestão. Um total de 21 ossículos básicos fazem parte do estômago de M. carcinus e estão divididos em sete categorias de acordo com suas funções presumíveis. O significado destas características morfológicas é discutido em termos de sua implicação no manejo alimentar que podem apoiar futuras explorações comerciais deste importante recurso pesqueiro. PALAVRAS-CHAVE: Pitu, aquicultura, sistema digestivo, estratégia alimentar. 209 VOL. 46(2) 2016: 209 - 218 ACTA AMAZONICA Foregut morphology of Macrobrachium carcinus (Crustacea, Decapoda, Palaemonidae) INTRODUCTION The aim of this study was to provide a detailed description and illustration of the foregut morphology The functional morphology of the foregut can provide in M. carcinus, conduct a comparative study with other useful information about the feeding habits of reptant palaemonid freshwater prawns, as well as to address the decapod crustaceans (Suthers 1984; Albertoni et al. relationships between foregut morphology and feeding 2003; Drum 2005). There is much information about behavior. The structural organization of the studied the decapod digestive tract, particularly concerning foreguts is compared with other palaemonid prawns and to economically important species, such as palinurids, the relationship between the foregut morphology and scyllarids and penaeids (Cox and Bruce 2003; Suthers individual feeding behaviour is discussed. and Anderson 2006; Abrunhosa and Melo 2008). Little information on the mouthparts or alimentary tract of the genus Macrobrachium Bate 1868 and other caridean MATERIALS AND METHODS prawns has been reported in the literature, as an example The freshwater prawn used in this study were captured larvae of M. rosenbergii De Man, 1879 (Abrunhosa and using an artisanal trap called “matapi”, baited with flour of Melo 2002) and M. amazonicum (Heller, 1862) (Queiroz babaçu palm fruits (Orbignya speciosa) deployed at depths et al. 2011) and adults of M. malcolmsonii (Milne between 1 and 3 m in the mouth of the Amazon River: Edwards, 1844) (Patwardhan 1935a), M. acanthurus Santana Island (00º03’40.9’’S and 051º08’46.6’’W), Rasa (Wiegmann, 1836) (Felgenhauer and Abele 1989) and Island (00º16’08.1’’S and 051º07’25.9’’W), Pequena Island M. carcinus (Lima et al. 2014). (00º15’20.0’’S and 051º18’10.6’’W) and Mazagão Velho The stomach of carideans prawns exhibits a gradual (00º15’39.9’’S and 051º20’ 42.3’W). reduction in the number and development of ossicles The stomachs from 10 adult (9-15 cm) and 10 juvenile (4-8 and, internal armature that may be more related to cm) Macrobrachium carcinus (Linnaeus, 1758), were removed the phylogenetic history of the Caridea than to diet and dissected under a stereomicroscope, and digested in 10% (Felgenhauer and Abele, 1989). KOH-solution for 45 min at 80 ºC. All calcified structures of In general, macrophagy in crustaceans has been the stomach were stained by adding alizarin red to the heated associated with both robust mouthparts and a well- potassium-solution for 10–15 minutes (Brösing 2002, Lima calcified foregut; reduction of these structures has 2010). After staining, the stomachs were washed in distilled been established for detritivory (Kunze and Anderson water and stored in 70% ethanol, then drawn with the aid of 1979). However, for some natant decapods, this is not a a camera lucida (K 400L, Motic, Causeway Bay, Hong Kong). consistent generality (Suthers 1984). Most penaeids such General foregut morphology was described according to the as Penaeus plebejus (Hess, 1865) and P. monodon Fabricius, nomenclature proposed by Mocquard (1883), Kunze and 1798 are more likely to be predators than scavengers Anderson (1979) and Felgenhauer and Abele (1989). Setae or detrital feeders, since they can capture small fish, was determined using binocular microscope (BA2010, Motic, small crabs, other penaeids and mollusks (Chong and Causeway Bay, Hong Kong) and nomenclature proposed by Sazekumar 1981; Suthers 1984). In general, the ossicles Garm (2004). of the gastric mill in the marine shrimps are less calcified than the mouthparts. It follows then that the mastication RESULTS may occur mostly in the mouthparts (Patwardhan 1935a; The foregut of M. carcinus is a thin-walled translucent Meiss and Norman 1977; Suthers 1984). organ comprised by a mouth, the buccal cavity, esophagus and The study of the stomach contents of Macrobrachium stomach with two well-differentiated chambers: the cardiac species has revealed numerous food items as algae, chamber with high volume and a smaller pyloric chamber. detritus, plant parts, small aquatic insects, juvenile The mouth is a transverse slit situated on the ventral side of prawns, small fish, and other animals, showing a the head and bounded in front by a massive labrum, behind clear omnivorous diet with an important carnivorous by a thin bilobed labium, and laterally by the mandibles. The component (Jimoh et al. 2011; Melo and Nakagaki 2013; mouth leads into a short buccal cavity that opens posteriorly Lima et al. 2014). The occurrence of animal components and dorsally into the short esophagus. The short esophagus indicates that Macrobrachium species and penaeids have (eso) opens into the cardiac chamber whose walls are mostly similar predation behavior; however, the absence of gastric membranous with numerous longitudinal folds forming the mill in Macrobrachium (lateral and dorsal teeth) suggests cardiac sac (Csac). This sac expands laterally and toward the a different mechanism of digestion in the genus (Lima posterior portion of the stomach, completely covering the et al. 2014). pyloric chamber (Figure 1). 210 VOL. 46(2) 2016: 209 - 218 LIMA et al. ACTA AMAZONICA Foregut morphology of Macrobrachium carcinus (Crustacea, Decapoda, Palaemonidae) In ventral view, the stomach of the M. carcinus shows the cardiac chamber strengthened by chitinous ossicles joined to each other by ligaments enabling their articulation, especially between the cardiac and pyloric chambers (Figure 2A, B, C). Internally, the cardiac chamber possesses setose lateral ridges (lr) (Figure 3B, C) and lateral valves that may aid in moving the food bolus toward the cardio-pyloric valve, but certainly are not capable of mastication. These folds or channels in the cardiac floor are supported by inferior lateral cardiac ossicles (IX) and show numerous and small simple setae randomly distributed in the internal face (Figure 3B, C). In the upper portion of the channel a dense and orderly row of long serrulate setae (su) forms a comb-like sieve that performs the first filtering process in the stomach (Figure 3B, C). The central portion of the cardiac floor is inclined upwards forming an elongated ventral triangular ridge (cfc - cardiac floor crest) bordered by dense row of long simple setae (ss) (Figure 3B, C). At the posterior part of the floor, flaps or valves covering the opening